Biodegradable polymers have very unique properties, such as their generally good biocompatibility, degradationity in the body, degradation products can be absorbed by the body or excreted through the body's normal physiological pathway, and is widely used in various biomedical fields, such as surgical sutures, bone fixation devices, bio-tissue engineering scaffold materials, and drug-controlled release carrier et. al. Among them, synthetic biodegradable polymers are of particular interest due to their low immunogenicity, their properties such as degradation and mechanical properties, and the like, can be easily controlled. Synthetic biodegradable polymers are mainly aliphatic polyester, polycarbonate, polyamino acid, polyphosphate, polyanhydride, poly orthoester and so on. Among them, polycarbonates such as polytrimethylene cyclic carbonate (PTMC), aliphatic polyester such as polyglycolide (PGA), polylactide (PLA), lactide-glycolide copolymer (PLGA), polycaprolactone (PCL) and so on are the most commonly used biodegradable polymers, has got the permission of the US Food and Drug Administration (FDA).
However, the existing biodegradable polymers such as PTMC, PCL, PLA and PLGA have simple structure, are lack of functional groups used for modification, thus the medical requirements are hardly satisfied. For example, the drug carriers or the surface modified coatings based on these polymers of these conventional carbonate monomers have fatal weakness of poor stability.
In recent years, many different types of functional biodegradable polymers have been reported in the literature. The researchers particularly interested in biodegradable polymers containing functional groups such as hydroxyl (OH), carboxyl (COOH), amino (NH2), mercapto (SH), etc., since polymers with these functional groups can directly bond drug and accept controlled and sustained release of the drug or the biocompatibility and bioactivity of the entire material can be improved by the attachment of some biologically active molecules to the polymer via functional groups. Functional biodegradable polymers are typically obtained by ring-opening polymerization of functional cyclic monomers, either by deprotection or by further modification. Degradation products of polycarbonate are mainly carbon dioxide and neutral glycol, do not produce acid degradation products. The functional cyclic carbonate monomer can be copolymerized with many cyclic ester monomers such as glycolide (GA), Lactide (LA), caprolactone (ε-CL), and other cyclic carbonate monomers to obtain biodegradable polymers with different properties.